After his miraculous healing, the man heads to the Temple, probably to praise and thank God for his wonderful blessing. There, Christ instructs him in the spiritual principle of overcoming sin. The Jews viewed the Temple, not only as a place of thanksgiving, but also one of spiritual teaching and learning. Similarly, worship on the Sabbath with others of like mind creates a place of essential spiritual instruction for living God's way of life. People who avoid formal worship of God miss out on vital instruction and will be spiritually unprepared for God's Kingdom.
The man's healing was instantaneous, but the learning is not. It is a long process that requires both instruction (hearing) and application (doing). It takes time to grow in grace and knowledge (James 1:23-25; II Peter 3:17-18; Isaiah 28:9-10), as well as patience and discipline.
Christ warns the healed man not to go back to sinful conduct, indicating that his crippled condition resulted from sin. All sickness is not caused by our own personal sin, as John 9 shows in the example of the man blind from birth. Sometimes ill health is the effect of our forebears' sins or the accumulated sins of a whole society.
Jesus' warning, "Sin no more, lest a worse thing come upon you," is always apt because human nature, especially when encouraged by Satan, easily degenerates into sin. The experience of renewed health should instill in us a deeper repulsion of sin, a greater watchfulness for its pitfalls, and a more purposeful determination to overcome it. When we experience healing, we would all do well to remember Christ's warning.